INTRODUCTION 



ARDLY any body of water or moist spot on the face of the 

 earth is devoid of algae. They are almost as nearly 

 ubiquitous as are the bacteria which are perhaps the 

 most widely distributed organisms in the world. The 

 variety of form and color exhibited by the algae is seem- 

 ingly endless and Nature has shown no bounds in designing these 

 ornate plants, many of which have bizarre shapes and specialized 

 habits. 



Because of the bright colors possessed by many algae and because 

 their extensive growths which develop in ponds and streams, algae 

 frequently attract attention. The more conspicuous growths of fresh- 

 water algae are usually referred to erroneously by the stranger as 

 "water moss," "moss," "frog-spittle," or are sometimes called "pond 

 scums." This illustrated key is designed to give the student who is 

 equipped with a microscope an opportunity to explore the world of 

 freshwater algae and to give the correct scientific name (at least the 

 genus name) to the more common forms. The student may find to 

 his surprise that a clot of "moss" will include half a dozen or more 

 distinct and recognizable plants, each with its own individual char- 

 acteristics of form, method of reproduction, and life history. In some 

 collections taken from acid bogs as many as 200 or more different 

 species may be found. 



It is hoped that this book will be a help in identifying the genera 

 of freshwater algae and that it will serve toward the elimination of the 

 indefinite and erroneous names under which they pass. To be sure, 

 the naming of a plant or an animal is not necessarily an end unto 

 'itself — but identification and naming must serve as a basis for a study 

 of structure, life history, ecological distribution and economic im- 

 portance. Just as when one knows the name of a person and so can 

 then learn more about him (or her), so the naming of algae can be 

 , the beginning of further investigation for the pure pleasure of getting 

 acquainted with the world of aquatic life about us, or for scientific 

 . pursuits. 



Having found the generic names of Ireshwater algae, the student 

 » may wish to identify the plants according to their specific names. For 

 this he will want to turn to some of the works listed in the bibliography. 

 An attempt has been made in illustrating the genera of algae to present 

 the most common species that one is likely to meet, or to give illustra- 

 tions of several species of a genus. In many cases, among the one- 

 celled and colonial genera especially, there is considerable variation 

 in form among the species contained in a genus. The student will 



